This invention relates to a position detector and more particularly to an improved position measuring apparatus and method of accurately locating components for use in placement apparatus such as chip mounters.
There is a considerable demand for devices that are capable of mounting or positioning small components such as integrated circuits, resistors, capacitors and the like at accurate locations on substrates such as printed circuit boards. This type of apparatus is generally referred to as a "chip" or "surface" mounter.
The components that are positioned are generally fed to the apparatus at a feeder location. Frequently, the components are positioned in specially-formed tapes that form individual pockets in which the components are received. Tape feeders present these components to a pickup device which then picks them up and positions them on the substrate.
At one time, these components were accurately positioned on the pickup apparatus by gripping fingers or other devices that physically engaged the component and would shift the component to a corrected position before placement. Many types of components do not, however, lend themselves to handling in this manner.
Therefore, a wide variety of types of non-contact sensors have been employed. These sensors sense the actual position of the component as picked up by the pickup device. By being able to determine the actual position of the component, then correction in its position can be made when the component is positioned on the substrate.
This invention deals primarily with such a non-contact type of sensing arrangement and method. One type of arrangement which is conventionally utilized for providing this sensing utilizes a plurality of laser-type light sources that operate through optical devices to cast a plurality of parallel light rays across a sensing station in which the component and its pickup device is positioned. A receptor is disposed on the other side of the pickup device and held component and a shadow is cast on that receptor. By rotating the component in the path of the light rays it is possible to measure from the shifting and size of the shadow the actual position of the component. These types of devices can be quite accurate.
However, they are also quite expensive. They require a plurality of laser light sources and frequently require in addition to a laser generator, a condenser lens, a mirror and a parallel light-forming lens all of which add to the cost of the apparatus.
It is, therefore, a principal object of this invention to provide an improved arrangement wherein a more simple light source can be employed for accurately determining the position of a component as picked up by a pickup device.
It is a further object of this invention to provide an improved low-cost sensor and sensing method for such applications.
In conjunction with the detecting of the component position and as has been noted, frequently a procedure is utilized that involves the rotation of the component and its pickup device in a sensing station. Although this procedure may be carried out during the time when the component is being transported, it nevertheless can be time-consuming. In addition, if the rotational movements are made rapidly or abruptly, they may actually cause the component to shift or in extreme cases become displaced from the pickup device.
It is, therefore, a still further object of this invention to provide an improved detecting method and apparatus for determining the position of a component which does not necessarily require rotation of the component.
It is a further object of this invention to provide an improved detecting apparatus and method wherein no relative movement need be required in order to provide a determination of the condition of the component relative to its pickup device.
One type of rotational methodology employed involves rotating the component to a position where the shadow which it casts has a minimum width. With rectangular components this permits determination of when an end of the component is perpendicular to the light sources. However since the initial position of the component may vary, the time to accomplish this step varies from component to component. Thus the apparatus must be capable of adjustment in its time sequence. This greatly complicates programming of the apparatus.
It is therefore a further object of this invention to provide a position determining method and apparatus that can operate on a fixed rather than variable time sequence.